X iv : h ep - p h / 97 10 38 3 v 1 1 7 O ct 1 99 7 Cosmological Relics of the High Energy Cold Dark Matter Particle in the Universe

We demonstrate that if the universe is dominated by the massive cold dark matter, then besides the generally believed thermal distribution of the dark matter relics, there may exist some very energetic non-thermal relics of the dark matter particles in the universe from some unknown sources, such as from decay of supermassive X particle released from topological defect collapse or annihilation. Very interesting, we point out that these high energy dark matter particles may be observable in the current and future cosmic ray experiments. There is a great deal of evidence to indicate that the dominant component of the universe matter density is dark matter. The most direct evidence for existence of dark matter is from the astronomical observation of velocities of the spiral galaxies [1]. In our own galaxy, for example, in order to explain the observation, a local dark matter density ρ = 0.3GeV/cm is determined [2]. In addition, the inflation theory predicts a flat universe, i.e. Ω = 1. The standard big-bang nucleosynthesis implies that the ordinary matter can contribute at most 15 percent of the critical density. It means that 90 percent of the matter in our universe may be dark [3]. The most attractive candidate of the dark matter is from the particle physics. One of them is the weakly-interacting massive particle (WIMP). The WIMP serves as a natural cold dark matter candidate to the universe, since if the WIMP is at a weak-scale mass it naturally provides a near closure density to the present universe as required by the inflation theory. In the present universe the WIMP dark matter particle is statically distributed. Its density is controlled by the Boltzman equation and the evolution of the universe, so it is called thermal relic abundance. So far experimental effort to search for the cold dark matter is made to find the signals of this distribution. The most promising experiments involve the direct detection at low background detectors, which look for the signal of dark matter particle as it collides with detector matter, and the indirect detection through observation of energetic neutrinos emerging from annihilation of cold dark matter particles which are accumulated in the Sun and the Earth [1]. Having not seen any signal in these experiments the parameter space of the WIMP models is seriously restricted. However to discover the WIMP dark matter particles or rule out the WIMP models much more efforts are needed, hopefully the next generation detectors will cover much larger parameter space of the WIMP models. Instead, in this letter we discuss another possibility to search for cold dark matter. We start from a question, whether there exists a significant flux of very energetic cold